Method of manufacturing curved composite structural elements

ABSTRACT

A method of manufacturing curved composite structural elements can include fabricating a web ply in a flat curve over a removable substrate and laying up the ply on a curved web surface of a manufacturing tool. The method also can include laying up a diagonal ply with fibers oriented at +/−45° from the centerline of the web surface. The method further can include cutting a unidirectional composite tape into segments and laying up the tape segments to form a cross ply with a fiber orientation normal to the centerline of the web surface. One or both edges of the diagonal and cross plies may be folded over one or two sides of the manufacturing tool to form one or two flange surfaces. Additionally, a cap ply can be laid up on one or both flange surfaces using composite tape. The structural element layup can then be inspected and any excess composite material can be trimmed away.

FIELD OF THE INVENTION

The present disclosure relates generally to composite structures. Moreparticularly, the present disclosure relates to manufacturingload-carrying structural elements from composite materials.

BACKGROUND OF THE INVENTION

Composite materials have been used increasingly in a variety ofindustries, including the automotive, marine and aerospace industries.Composite materials have been used to produce nonload-carryingstructures, such as boat hulls or automobile body panels. Compositematerials have also been applied in the manufacture of load-carryingstructures, such as pressure vessels and aircraft fuselages.

Composite materials especially have application in the design ofstructural members carrying tensile loads. Composite materials used inthese designs include strong fibrous materials, such as carbon, aramid,glass or quartz, bonded together with a resin material, such as anepoxy. Such materials can have the advantage of a high tensile strengthto weight ratio, permitting the design of lightweight structures havingsubstantial strength in tension. Since the load in these materials iscarried primarily by the fibers, a variety of composite materials havebeen developed with unidirectional fibers, that is, the fibers aresubstantially aligned in a uniform direction. Thus, these materials arefrequently used in designs that place the fibers along the direction ofthe tensile load in a structural member.

However, the composite material designs can have the disadvantage thatthe unidirectional fibers do not follow the contour of the structuralmember. For example, in a structural element that includes a surfacethat is curved within a plane, the composite material can be trimmed tothe shape of the planar arc, but the fibers do not follow the curve ofthe arc. In such a design, the orientation of the unidirectional fibersdoes not lie in the direction of loading in the structural member.Furthermore, the unidirectional fibers are severed along the trimmededge of the curve.

Accordingly, it is desirable to provide a method of manufacturing curvedcomposite structural elements with load-bearing fibers aligned along thecurvature of the structural element.

SUMMARY OF THE INVENTION

The foregoing needs are met, to a great extent, by the presentinvention, wherein in one aspect a method is provided that in someembodiments permits the semi-automated manufacture of curved compositestructural elements with load-bearing fibers aligned along the curvatureof the structural element using a combination of fiber placement andmanual or automated layup processes.

In accordance with one aspect of the present invention, a method offabricating a composite curved ply can include placing a plurality ofcontiguously adjoined strips of a composite material in the shape of aplanar arc to form a ply. The strips may be placed on a removablesubstrate material. The composite material can include a plurality offibers having a general fiber orientation, and the fiber orientation ofeach of the strips can be substantially aligned along the full length ofthe planar arc. In addition, the method can include trimming an edge ofthe ply.

In accordance with another aspect of the present invention, a method ofmanufacturing a composite curved structural element can include the stepof laying up a curved composite web ply including a composite materialon a manufacturing tool that includes a curved surface in the shape of aplanar arc. The composite material can comprise a plurality of fibersincluding a general fiber orientation, and the fiber orientation of theweb lay can be substantially aligned with a longitudinal centerline ofthe curved surface. The method further can include the step of curingthe web ply.

In accordance with yet another aspect of the present invention, a methodof manufacturing a composite curved structural element can include thestep of laying up a diagonal ply including a composite material on amanufacturing tool that includes a curved surface in the shape of aplanar arc. The composite material can comprise a plurality of fibersincluding a first fiber orientation and a second fiber orientation.Additionally, the first and second fiber orientations of the diagonalply can form angles with a tangent of a longitudinal centerline of thecurved surface that are approximately constant at all points along thelongitudinal centerline. The method further can include the step ofcuring the web ply.

In accordance with still another aspect of the present invention, amethod of manufacturing a composite curved structural element caninclude the steps of cutting a segment of a composite tape that has aplurality of tape fibers with a general tape fiber orientation andlaying up a cross ply including the tape segment on a manufacturingtool. The manufacturing tool can include a curved surface in the shapeof a planar arc. Additionally, the tape fiber orientation cansubstantially form a right angle with a tangent of a longitudinalcenterline of the curved surface at all points along the longitudinalcenterline.

There has thus been outlined, rather broadly, certain embodiments of theinvention in order that the detailed description thereof herein may bebetter understood, and in order that the present contribution to the artmay be better appreciated. There are, of course, additional embodimentsof the invention that will be described below and which will form thesubject matter of the claims appended hereto.

In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of embodiments inaddition to those described and of being practiced and carried out invarious ways. Also, it is to be understood that the phraseology andterminology employed herein, as well as the abstract, are for thepurpose of description and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conceptionupon which this disclosure is based may readily be utilized as a basisfor the designing of other structures, methods and systems for carryingout the several purposes of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view illustrating a curved structural elementwith a “C”-shaped cross section.

FIG. 1B is a perspective view illustrating a curved structural elementwith an “L”-shaped cross section.

FIG. 2 is a perspective view illustrating a manufacturing tool, ormandrel, in accordance with an embodiment of the method or process.

FIG. 3 is a perspective view illustrating a fabrication and layupprocess of a 0-degree web ply of a composite material.

FIG. 4 is a perspective view illustrating the layup of a 0-degree capply of a composite material.

FIG. 5 is a perspective view of the layup of a 45-degree diagonal ply ofa composite material on a manufacturing tool.

FIG. 6 is a perspective view illustrating the layup of a 90-degree crossply of a composite material.

FIG. 7 is a perspective view illustrating a structural element layupthat has been transferred onto a concave manufacturing tool.

FIG. 8 is a perspective view illustrating the enclosure of a structuralelement layup in a sealed vacuum bag for curing.

FIG. 9 is a flowchart illustrating steps that may be followed tomanufacture a curved composite structural element.

DETAILED DESCRIPTION

An embodiment in accordance with the present disclosure provides amethod of manufacturing curved composite structural elements. The methodcan include fabricating a composite curved web ply using an advancedfiber placement (AFP) machine such that the fiber orientation of thecomposite material is substantially aligned with the curvature of thestructural element. The web ply can then be trimmed and laid up on amanufacturing tool having a curved surface to match the shape of the webply.

The method also can include laying up a diagonal ply of composite fabricwith the fabric fibers oriented at 45 degrees from a tangent of thecenterline of the curved surface. The method further can include layingup a cross ply composed of composite tape segments with the tape fibersoriented at a right angle to the tangent of the centerline of the curvedsurface. In addition, one or both edges of the diagonal ply and thecross ply may be folded over a side of the manufacturing tool to form acap surface.

Furthermore, the method can include laying up a cap ply composed ofcomposite tape with the fiber orientation aligned with the centerline ofa cap surface of the manufacturing tool. The structural element layupmay then be sealed in a vacuum bag to allow the composite material tocure, after which the structural element may be inspected and excessmaterial may be trimmed away. This method of manufacture of a compositestructural element has an advantage in that the web ply fibers areoriented in alignment with the curvature of the structural element alongits entire length.

An embodiment of the disclosure will now be described with reference tothe drawing figures, in which like reference numerals refer to likeparts throughout. An example of a composite structural element 102 witha curved planar surface, or web surface, 104 and two side, or cap,surfaces 106, 108 forming a “C”-shaped cross section that may beproduced by a method of an embodiment of the disclosure is shown in FIG.1A. Similarly, FIG. 1B shows an example of a composite structuralelement 110 with a curved planar surface, or web surface, 104 and oneflange, side or cap surface 106, including several cutaways, or “mouseholes,” 112 that may be produced using a method of an embodiment of thepresent disclosure. These two exemplary structural elements 102, 110correspond to an embodiment of a first frame section, or shear tie,(110) and an embodiment of a second frame section, or floating frame,(102) used as structural support elements in an aircraft fuselage.Examples of these components are found in copending U.S. patentapplication Ser. No. 10/851,381, Biornstad et al., “Composite BarrelSections for Aircraft Fuselages and other Structures, and Methods andSystems for Manufacturing such Barrel Sections,” filed May 20, 2004, andSer. No. 10/853,075, Johnson et al., “Structural Panels for Use inAircraft Fuselages and other Structures,” filed May 25, 2004, thedisclosures of which are hereby incorporated in their entirety. However,alternative embodiments of this disclosure may be used to produce anycompatible load carrying element, including stiffeners, beams andframes, such as those used in pressure vessels, other compositecontainers, boats, trains, submersibles, arches, buildings, bridges,seismic upgrades, window frames or door frames.

In an embodiment of the present disclosure, structural elements aremanufactured from a composite material, for example, a polymer matrix,epoxy, BMI or a polyester thermosetting plastic, such as PEEK, PEKK, orPPS reinforced with fibers, such as carbon, aramid, glass, Kevlar,boron, Hybor or quartz, possibly intermixed with metal, metal foil, suchas TiGr, or fiber metal laminate. These composite materials generallyare “cured” into a stronger form through an endothermic chemicalreaction, which requires the addition of energy, for example, by way ofheating or irradiation. Examples of composite materials used in variousembodiments of this disclosure include graphite fiber reinforced epoxy,fiber reinforced plastic (FRP), glass-fiber reinforced plastic (GRP),carbon-fiber reinforced plastic (CRP), metal matrix composites (MMC),and reinforced carbon-carbon (carbon fiber in a graphite matrix).

An embodiment of the present disclosure can include a hand, or manual,layup process, or an automated layup process, wherein a compositematerial, such as a composite fabric or a composite tape, is placed on amanufacturing tool. An exemplary embodiment of a manufacturing tool, ormandrel 200, is illustrated in FIG. 2. An exemplary mandrel 200 caninclude a web surface 202, which corresponds to the curved planarsurface 104 of the structural element 102, 110 shown in FIG. 1A and FIG.1B. The exemplary mandrel 200 also can include an inner side, or cap,surface 204; an outer side, or cap, surface 206; or both inner and outerside, or cap, surfaces 204, 206. In other embodiments, the exemplarymandrel 200 can include a near-endless combination of other surfaces.

An embodiment of the present disclosure can include a fiber placementprocess, in which an advanced fiber placement (AFP) machine can be usedto fabricate a curved web ply of a structural element. As known in theart, the fiber placement process typically involves the automatedplacement of multiple “tows” (that is, untwisted bundles of continuousfilaments, such as carbon or graphite fibers, pre-impregnated with athermoset resin material such as an epoxy commonly known as “prepregtow”) or slit composite tape (“slit tape”) onto a manufacturing tool, ormandrel. Conventional fiber placement machines dispense multiple tows toa movable payoff head that collimates the tows (that is, renders thetows parallel) and applies the tows to a mandrel surface using one ormore compaction rollers that compress the tows against the surface. Atypical tow is between about 0.12 inch and 0.25 inch wide whenflattened. In addition, such machines typically include means fordispensing, clamping, cutting and restarting individual tows duringplacement.

Slit tape is a composite tape that has been slit after being produced instandard widths by the manufacturer. Slitting the tape results innarrower widths that allow enhanced maneuverability and tailoring duringapplication in order to achieve producibility and design objectives. Forexample, in a particular embodiment, a 12-inch wide tape is cut intoninety-six even slits of ⅛ inch each. Generally, slit tape can havewidths varying from about 0.12 inch up to about six inches, and may ormay not include backing paper.

An exemplary embodiment of a fiber placement process 300 according tothe present disclosure is illustrated in FIG. 3. In this exemplaryembodiment, an advanced fiber placement (AFP) machine 302 can laycontiguously adjoined strips 304 of a composite material, either slittape or prepreg tow, in a planar arc 306, that is, in the shape of acurve on a flat surface. As a result, the fibers of the slit tape or toware oriented in alignment with the longitudinal centerline of the arcalong the full length of the curve without distortion of the fibers,such as wrinkles. In a particular embodiment, the curved structuralelement includes the shape of a planar arc with uniform radius.Nevertheless, other embodiments include structural elements with acurvature of nonuniform radius, or a complex contour that does not liein a plane. In a particular embodiment of this disclosure, rather thanbeing placed directly onto a mandrel, the strips 304 of compositematerial are placed over a removable substrate, such as mylar, which maybe attached, for example, to a metal caul plate. In an alternativeembodiment, the AFP machine 302 can place multiple plies, one overanother, creating a thicker grade ply.

Various processes of the present disclosure also can include a web plytrimming process, in which a web ply can be trimmed to remove excesscomposite and substrate material from the edges of the web ply. Forexample, in an exemplary embodiment of a web ply trimming process, anumerically-controlled ply cutting machine can cut a web ply to conformto the shape of a perimeter of a possibly curved web surface of amandrel or other similar manufacturing tool, such as that shown in FIG.2.

An embodiment of the present disclosure can also include a web ply layupprocess, in which a web ply is manually or automatically placed on amandrel, or other manufacturing tool, such as that shown in FIG. 2. Anexemplary embodiment of a web ply layup process 308 according to thepresent disclosure also is illustrated in FIG. 3. In this exemplaryembodiment, a web ply 310 such as that fabricated in the fiber placementprocess 300 can be placed on mandrel 200 using a manual or automatedlayup process. The web ply 310 can be oriented on the curved web surface202 of the mandrel such that the composite fibers are aligned with thecenterline of the curved surface along the full length of the arc. Theweb ply 310 is generally referred to as a 0-degree ply, a namingconvention referencing the angle of the fibers with respect to thecenterline of the surface. The substrate material can then be removedfrom the surface of the web ply 310. In an alternative embodiment, theweb ply 310 can be laid up over a previous ply, which may be a web plyor another type of ply, on the mandrel 200.

In an alternative embodiment of the present disclosure, a cap ply layupprocess 400, i.e., a process where a cap ply is manually orautomatically placed on a mandrel (or other manufacturing tool) such asthat shown in FIG. 2, can be used. FIG. 4 depicts an example of a capply layup process 400 according to the present disclosure. In thisexample, a cap ply 402 can be laid up on the exemplary mandrel or othermanufacturing tool, such as that shown in FIG. 4. The cap ply 402 canconsist of a composite tape, for example, approximately two inches wide,and can be placed on a mandrel 200 such that the orientation of the tapefibers runs in a lengthwise, or substantially 0-degree, direction alongthe cap surface 106. As further shown in FIG. 4, a single cap ply 402 or404 can be laid up on one side of the mandrel 200 in order to form an“L”-shaped cross section with a single flange, such as that of theexemplary structural element in FIG. 1B, and a second cap ply 404 or 402can be applied to the opposite side of the mandrel 200 in order to forma “C”-shaped cross section with two flanges, such as that of theexemplary structural element in FIG. 1A.

In the case of either or both cap plies 402 and 404 splices 406 and 408can be formed along the corner of the mandrel 200 where the cap ply 402and 404 meets the web ply 310. In this way, the cap ply or plies 402 and404 and the web ply form a continuous, substantially 0-degree ply acrossthe web surface 202 and one or both cap surfaces 106 and 108. Since thesplices 406 and 408 do not interrupt the 0-degree fibers along thelength of the web and cap surfaces, which are designed to carry tensileloads in the longitudinal direction of the web and cap surfaces, thesplices 406, 408 do not affect the load-bearing capacity of thestructural elements 102 and 110. An alternative embodiment of thedisclosure can include 0-degree cap plies 402 and 404, without a0-degree web ply 310.

In yet another exemplary embodiment of the present disclosure, adiagonal ply layup process 500 wherein a diagonal ply can be manually orautomatically placed on a mandrel is depicted in FIG. 5. In thisexample, a diagonal ply 502 can be placed on the mandrel 200 so that thefibers are oriented on the bias at approximately positive (+) andnegative (−) 45 degrees from the centerline of the web surface of themandrel 200. The composite fabric 504 in a present embodiment is aprepreg composite fabric pre-impregnated with a resin. However, in otherembodiments, the composite fabric 504 may include any suitable type ofcomposite fabric, including a dry form composite fabric. Although thediagonal ply shown in FIG. 5 includes a sheet of composite fabric 504,an alternative embodiment can include a diagonal ply formed from stripsof composite tape laid up on the mandrel 200 so that the tape fibers areoriented at approximately +45 degrees or −45 degrees from the centerlineof the web surface of the mandrel. Furthermore, alternative embodimentscan include a diagonal ply with the fibers oriented on a bias at anyangle between 0 and 90 degrees from the centerline of the web surface,for example, at positive and negative 60 degrees.

In order to form the flange, side, or cap, surfaces of the structuralelement, the material of the diagonal ply 502 is cut wider than the websurface 202 of the mandrel 200 so that at least one edge of the diagonalply 502 can be folded over the side of the mandrel 200. A single edge ofthe diagonal ply 502 can be folded over the outer cap surface 206 of themandrel 200 in order to form an “L”-shaped cross section, such as thatof the example structural element shown in FIG. 1B. Alternatively, inorder to prevent or minimize wrinkling, the diagonal ply 502 can befirst placed on the inner cap surface 204 of the mandrel 200 and thenfolded over the curved web surface 202 by tensioning and uniformlyspreading the fibers across the curved web surface 202 to form an“L”-shaped cross section. In addition, the diagonal ply 502 optionallycan be folded over the outer cap surface 206 of the mandrel 200, inorder to form a “C”-shaped cross section, such as that of the examplestructural element shown in FIG. 1A. Similarly, the diagonal ply 502 canbe first placed on the curved web surface 202 by tensioning anduniformly spreading the fibers across the curved web surface 202 andthen folded over the outer cap surface in order to form an “L”-shapedcross section, such as that of the example structural element shown inFIG. 1B.

Other embodiments of the present disclosure can include a cross plylayup process 600, i.e., a process where a ply is placed in a fashionsimilar to that shown in FIG. 6. First, a unidirectional composite tape602 is cut into segments. For example, the tape can be cut intotrapezoidal segments 604, as shown in FIG. 6. For the purposes of thisdisclosure, the term “trapezoidal” is used in the sense of its commonmeaning in American English, with reference to a quadrilateral havingonly two sides parallel, as opposed to the common meaning in BritishEnglish, with reference to a quadrilateral having no two sides parallel.The term commonly used in British English for a quadrilateral havingonly two sides parallel is “trapezium.”

Returning to FIG. 6, the two non-parallel sides of the trapezoidal tapesegments 604 can be cut at an angle such that when laid up on themandrel 200 the two non-parallel edges of the tape segment will besubstantially perpendicular to the tangent of the longitudinalcenterline of the curved or web surface 202 of the mandrel 200. The tapesegments 604 then can be laid up on the exemplary mandrel 200 in orderto form a cross ply 606 with fibers oriented approximately at a rightangle with the centerline of the web surface 202 of the mandrel 200,without forming wrinkles in the tape segments 604.

As in the diagonal ply example described above, the cross ply 606 can becut wider than the web surface of the mandrel 200 such that one or twoedges of the cross ply 606 can be folded over the side or sides of themandrel 200 in order to form flange, side, or cap, surfaces. In oneembodiment, the tape can be cut into modified “funnel” shape segments608, such that the edge or edges of the tape segment 608 that fold overthe cap surfaces 204, 206 of the mandrel 200 have parallel sides and theportion over the web surface 202 of the mandrel 200 has nonparallelsides. In an alternative embodiment, the tape can be cut intorectangular segments and allowed to overlap or to form gaps between thetape segments when laid up on the mandrel 200. Once again, in this way a“C”-shaped cross section or an “L”-shaped cross section can be formed.

Alternatively, in order to prevent or minimize wrinkling, the cross ply606 can be first placed on the inner cap surface 204 of the mandrel 200and then folded over the curved web surface 202 by tensioning anduniformly spreading the fibers across the curved web surface 202 inorder to form an “L”-shaped cross section. In addition, the cross ply606 optionally can also be folded over the outer cap surface 206 of themandrel 200, in order to form a “C”-shaped cross section, such as thatof the example structural element shown in FIG. 1A. Similarly, the crossply 606 can be first placed on the curved web surface 202 by tensioningand uniformly spreading the fibers across the curved web surface 202 andthen folded over the outer cap surface in order to form an “L”-shapedcross section, such as that of the example structural element shown inFIG. 1B.

FIG. 7 illustrates a transfer process 700, in which a structural elementlayup is transferred from a convex mandrel (or other manufacturing tool)to a concave manufacturing tool 702. In the present example of FIG. 7 aconcave manufacturing tool 702, or female mandrel, is illustrated. Inthis example, structural element plies previously allowed to cure aslaid up on a convex manufacturing tool, such as the exemplary mandrel200 of FIG. 2, may be optionally transferred to a concave manufacturingtool 702 for curing. In the present embodiment the concave manufacturingtool 702 conforms to the external surface of the structural elementlayup.

In an alternative embodiment, plies can be laid up directly on a concavemanufacturing tool, such as that shown in FIG. 7, rather than being laidup on a convex manufacturing tool. In this case, the plies can beallowed to cure as laid up on the concave manufacturing tool, oroptionally transferred to and cured on a convex tool.

Another exemplary process of the present disclosure can include asealing process, in which a structural element layup is sealed inside avacuum bag in order to remove trapped air from inside and underneath acomposite material, between layers of composite plies and between acomposite material and a respective mandrel. An exemplary embodiment ofa vacuum bag 802 encasing a structural element on an exemplary mandrel200 layup is illustrated in FIG. 8. Similarly, a exemplary embodiment ofa vacuum bag 704 encasing a structural element layup on a concavemanufacturing tool 702 is illustrated in FIG. 7.

FIG. 9 is a flowchart outlining an exemplary method according to thepresent disclosure for manufacturing a curved composite structuralelement. The process starts in step 902 where an advanced fiberplacement (AFP) machine lays contiguously adjoined strips of a compositematerial. As discussed above, in various embodiments the compositematerial can be in the form of either slit tape or prepreg tow.Additionally, as discussed above, the AFP machine can place the stripsin any number of viable or useful shapes, such as the exemplary planararc shown in FIG. 3, with the fibers of the slit tape or tow oriented inalignment with the longitudinal centerline of the arc along the fulllength of the curve, without distortion of the fibers, such as wrinkles.As further discussed above, the strips of composite material can beplaced over a removable substrate, such as mylar. Furthermore, in analternative embodiment the AFP machine can place multiple plies, oneabove another, creating a thicker grade ply. The process continues tostep 904.

In step 904, a web ply can be trimmed to remove excess composite andsubstrate material from the edges of the web ply. In this step, anumerically-controlled ply cutting machine can cut the web ply to theshape of the perimeter of the web, or curved, surface of a mandrel, orother similar manufacturing tool, such as that shown in FIG. 2. Next, instep 906, web ply can be laid up on a mandrel, or other similarmanufacturing tool, such as that shown in FIG. 2. The web ply can belaid up using a manual or automated layup process, orienting thecomposite fibers in a 0-degree direction aligned with the centerline ofthe curved web surface of the mandrel or other tool along the fulllength of the arc, such as the web ply shown in FIG. 3. In addition, thesubstrate material can be removed from the surface of the web ply duringthis step. In various embodiments, a web ply can be laid up directly onthe mandrel or other tool, or alternatively, over a previous ply orcombination of plies on the mandrel or other tool. In addition, variousembodiments may include more than one web ply in combination with otherplies. The process continues to step 908.

In step 908, a cap ply can be manually or automatically laid up on amanufacturing tool, such as the mandrel shown in FIG. 2. As discussedabove, the cap ply can consist of composite tape, and can be placed onthe mandrel or other tool such that the orientation of the tape fibersruns in a lengthwise, or 0-degree, direction along the cap surface, suchas the exemplary cap ply layup shown in FIG. 4. A single cap ply can belaid up on one side of the mandrel or tool in order to form an“L”-shaped cross section with a single flange, such as that of theexample structural element shown in FIG. 1B, plus a second cap ply canbe applied to the opposite side of the mandrel in order to form a“C”shaped cross section with two flanges, such as that of the examplestructural element shown in FIG. 1A, forming a continuous 0-degree plyacross the web surface and one or both cap surfaces. In variousembodiments, a cap ply can be laid up directly on the mandrel or othertool, or alternatively, over a previous ply or combination of plies onthe mandrel or other tool. In addition, various embodiments may includemore than one cap ply in combination with other plies. The processcontinues to step 910.

In step 910, a +/−45-degree diagonal ply of composite fabric can bemanually or automatically laid up on a mandrel, or other similarmanufacturing tool, such as that shown in FIG. 2. The diagonal ply canbe placed on the mandrel or other tool so that the fabric fibers areoriented at approximately +/−45 degrees from the centerline of the websurface of the mandrel or other tool, such as the diagonal ply shown inFIG. 5. As discussed above, in various embodiments the composite fabriccan take the form of any suitable composite fabric, including a prepregcomposite fabric pre-impregnated with a resin. In various embodiments, adiagonal ply can be laid up directly on the mandrel or other tool, oralternatively, over a previous ply or combination of plies on themandrel or other tool. In addition, various embodiments may include morethan one diagonal ply in combination with other plies. The processcontinues to step 912.

In step 912, in order to form side, or cap, surfaces of the structuralelement the composite fabric of the diagonal ply can be cut wider thanthe web surface of the mandrel or other tool so that at least one edgeof each diagonal ply can be folded over the side of the mandrel or othertool. A single edge of the diagonal ply can be folded over one side ofthe mandrel or other tool in order to form an “L”-shaped cross section,such as that of the example structural element shown in FIG. 1B, or twoedges of the diagonal ply can be folded over two sides of the mandrel orother tool in order to form a “C”-shaped cross section, such as that ofthe example structural element shown in FIG. 1A. Alternatively, in orderto prevent or minimize wrinkling of the composite fabric over the innercap surface of the mandrel, the diagonal ply can be first adhered to theinner cap surface and then folded over the web surface, stretching thecomposite fabric as necessary to prevent or minimize wrinkling on thecap surface or on the web surfaces. In addition, the diagonal ply canthen be folded over the outer cap surface, stretching the compositefabric as required to prevent or minimize wrinkling on the web surfaceor on the outer cap surface. The process continues to step 914.

In step 914, a unidirectional composite tape can be cut into segments,such as the exemplary tape segments shown in FIG. 6. Next, in step 916,the tape segments can be manually or automatically laid up on a mandrelor other similar manufacturing tool. As discussed above, the fibers ofthe tape segments can be aligned at substantially 90 degrees with thecenterline of the web surface of the mandrel or other tool in order toform a 90-degree cross ply. In the case of trapezoidal or modified“funnel” shape tape segments, the fibers can be oriented approximatelyat a right angle with the centerline of the web surface of the mandrelor other tool, without overlapping or creating gaps between the tapesegments, and without forming wrinkles in the tape.

As in the case of the diagonal ply above, the cross ply can be cut widerthan the web surface of the mandrel or other tool, and one or two edgesof the cross ply can be folded over the side or sides of the mandrel orother tool in order to form side or cap surfaces. Once again, in thisway a structural element with a “C”-shaped cross section or an“L”-shaped cross section can be formed. In various embodiments, a crossply can be laid up directly on the mandrel or other tool, oralternatively, over a previous ply or combination of plies on themandrel or other tool. In addition, various embodiments may include morethan one cross ply in combination with other plies. The process thencontinues to step 918.

In step 918, the structural element layup may optionally be transferredto a concave manufacturing tool, e.g., a female mandrel. As discussedabove, the concave tool or mandrel can conform to the external surfaceof the structural element layup, as shown in FIG. 7. Next, in step 920,the structural element layup can be allowed to cure while sealed insidea vacuum bag on a mandrel or other tool, as shown in FIG. 8, or on aconcave tool or mandrel, as shown in FIG. 7. As discussed above, thevacuum can remove trapped air from inside the composite material andfrom underneath the composite material, between layers of the compositeplies and between the composite material and the mandrel. The processcontinues to step 922.

In step 922, after the structural element layup has cured, it can beinspected to verify compliance with the design specifications. Next, instep 924, the structural element layup can be trimmed, if necessary, toremove any excess material. In addition, cutouts, or “mouse holes,” suchas those shown in FIG. 1B, can be trimmed into the structural element.Control continues to step 926 where the process stops.

The example embodiment of the flowchart in FIG. 9 described aboveincludes only one web ply, one cap ply, one diagonal ply, and one crossply. However, other embodiments may include any number of plies in anycombination laid up in any order. For example, a floating frame with a“C”-shaped cross section, such as the exemplary structural element shownin FIG. 1A, can include eighteen plies on the web surface andtwenty-eight plies on each of the two cap surfaces. In this embodiment,the method could include laying up half of the plies in the followingorder:

-   -   a 45-degree diagonal ply on the web and both cap surfaces    -   a cap ply on each of the two cap surfaces    -   an additional cap ply on each of the two cap surfaces    -   a web ply on the web surface and a cap ply on the two cap        surfaces    -   a 45-degree diagonal ply on the web and cap surfaces    -   a cap ply on each of the two cap surfaces    -   an additional cap ply on each of the two cap surfaces    -   a 45-degree diagonal ply on the web and cap surfaces    -   a cross ply on the web and cap surfaces    -   a 45-degree diagonal ply on the web and the cap surfaces    -   a cap ply on each of the two cap surfaces    -   a 45-degree diagonal ply on the web and cap surfaces    -   a cross ply on the web surface and on the two cap surfaces    -   a 45-degree diagonal ply on the web and cap surfaces        The second half of the plies on the web surface and each of the        cap surfaces in this example could then be laid up on the        mandrel in the opposite order of the first half to form a mirror        image, or symmetrical, layup order, for a total of eighteen        plies on the web surface and twenty-eight plies on each of the        two cap surfaces.

Another example structural element with a “C”-shaped cross section, suchas the exemplary structural element shown in FIG. 1A, can include thesame ply combination as the previous example, except that the twolongitudinal extremes of the web surface each can include an additionalten plies covering the last twelve inches of the web surface at eachextreme of the structural element. In this embodiment, two additionaldiagonal plies can be laid up on the web surface at each extreme of thestructural element simultaneously with the two cap plies after the first45-degree diagonal ply, and before the first 0-degree web ply, of theprevious example.

In addition, two additional cross plies can be laid up on the websurface at each extreme of the structural element simultaneously withthe two cap plies after the second diagonal ply, and before the thirddiagonal ply, of the previous example. Furthermore, a 0-degree web plycan be laid up simultaneously with the cap ply before the final threeplies of the previous example. Similarly, a symmetrical ply order can beobtained by laying up an additional 0-degree web ply, two additionalcross plies, and two additional diagonal plies in the opposite orderbetween the second half plies of the previous example.

In this last example, each of the additional plies (of the first half ofthe symmetrical layers) can extend, for example, one half inch farthertoward the center of the structural element than the previous. That is,for example, the first additional 45-degree diagonal ply can extendtwelve-and-a-half inches from each end of the structural element layup;the second additional 45-degree diagonal ply can extend thirteen inchesfrom each end of the layup; the first additional cross ply can extendthirteen and a half inches from each end of the layup; the secondadditional cross ply can extend fourteen inches from each end of thelayup; and the additional web ply can extend fourteen-and-a-half inchesfrom each end of the layup. In order to form a symmetrical, or mirrorimage, layup order, the five additional plies of the second half of thesymmetrical layers each can extend one half inch less than the previous.

As a further example, a shear tie with an “L”-shaped cross section, suchas the exemplary structural element shown in FIG. 1B can includetwenty-four plies. In this embodiment, the method can include laying uphalf of the plies in the following order:

-   -   a 45-degree diagonal ply on the web and both cap surfaces    -   a cross ply on the web and cap surfaces    -   a 45-degree diagonal ply on the web and cap surfaces    -   a web ply on the web surface and a cap ply on the two cap        surfaces    -   a 45-degree diagonal ply on the web and the cap surfaces    -   a cross ply on the web surface and on the two cap surfaces    -   a 45-degree diagonal ply on the web and the cap surfaces    -   a web ply on the web surface and a cap ply on the two cap        surfaces    -   a 45-degree diagonal ply on the web and cap surfaces    -   a cross ply on the web surface and on the two cap surfaces    -   a 45-degree diagonal ply on the web and cap surfaces    -   a web ply on the web surface and a cap ply on the two cap        surfaces        The second half of the plies in this example can then laid up on        the mandrel in the opposite order of the first half to form a        mirror image, or symmetrical, layup order, for a total of        twenty-four plies on the web surface and on each of the two cap        surfaces.

The many features and advantages of the invention are apparent from thedetailed specification, and thus, it is intended by the appended claimsto cover all such features and advantages of the invention which fallwithin the true spirit and scope of the invention. Further, sincenumerous modifications and variations will readily occur to thoseskilled in the art, it is not desired to limit the invention to theexact construction and operation illustrated and described, andaccordingly, all suitable modifications and equivalents may be resortedto, falling within the scope of the invention.

What is claimed is:
 1. A method comprising the steps of: forming a0-degree, planar curved web ply of contiguous, adjoined fiber compositestrips by placing the strips to lay contiguously adjoined on a flatsurface and in the shape of a planar arc so that the fibers are in a0-degree direction aligned with a full length of a longitudinalcenterline of the planar arc without distortion; trimming the web ply toconform to the shape of a perimeter of a planar curved web surface of amandrel, said mandrel having first and second side cap surfaces whichmeet the web surface to form first and second corners respectively;laying up the web ply onto the web surface of the mandrel to have0-degree fiber orientation substantially aligned with the full length ofa longitudinal centerline of the web surface; and laying up a 0-degreecap ply of fiber composite tape onto the first cap surface to form asplice with the web ply along the first corner of the mandrel, the tapecomprising a plurality of tape fibers having 0-degree fiber orientationsubstantially aligned with a longitudinal centerline of the first capsurface, and the splice forming a continuous, substantially 0-degree plylying across the web surface and the first cap surface.
 2. The method ofclaim 1, further comprising laying up a 0-degree cap ply of fibercomposite tape onto the second cap surface to form a second splice withthe web ply along the second corner of the mandrel, the tape comprisinga plurality of tape fibers having 0-degree fiber orientationsubstantially aligned with a longitudinal centerline of the second capsurface, and the second splice forming a continuous, substantially0-degree ply lying across the web surface and the first and second capsurfaces.
 3. The method of claim 2, further comprising forming a curvedcomposite structural element by curing the resulting layup comprisingthe splices.
 4. The method of claim 3, wherein the curved compositestructural element is an aircraft structural member.
 5. The method ofclaim 4, wherein the aircraft structural member is a floating frame. 6.The method of claim 3, wherein the curved composite structural elementcomprises a C-shaped cross section.
 7. The method of claim 1, furthercomprising forming a curved composite structural element by curing theresulting layup comprising the splice.
 8. The method of claim 7, whereinthe curved composite structural element is an aircraft structuralmember.
 9. The method of claim 8, wherein the aircraft structural memberis a shear tie.
 10. The method of claim 7, wherein the curved compositestructural element comprises an L-shaped cross section.
 11. The methodof claim 1, wherein each strip is a slit composite tape.
 12. The methodof claim 1, wherein each strip is a prepreg tow.
 13. The method of claim1, wherein the web ply is formed on a removable substrate material. 14.The method of claim 13, further comprising removing the removablesubstrate material from the trimmed web ply subsequent to laying up theweb ply on the web surface of the mandrel.
 15. The method of claim 1,further comprising laying up a diagonal ply over the web surface of themandrel.
 16. The method of claim 15, further comprising laying up across ply over the web surface of the mandrel.
 17. The method of claim16, further comprising the steps of: sealing the resulting layupcomprising the splice, the diagonal ply, and the cross ply within avacuum bag to remove trapped air; and forming a curved compositestructural element by curing the sealed layup.
 18. The method of claim17, further comprising inspecting the curved composite structuralelement for defects.
 19. The method of claim 18, further comprisingtrimming the curved composite structural element.
 20. The method ofclaim 1, further comprising the steps of: sealing the resulting layupcomprising the splice within a vacuum bag to remove trapped air; andforming a curved composite structural element by curing the sealedlayup.
 21. The method of claim 20, further comprising inspecting thecurved composite structural element for defects.
 22. The method of claim21, further comprising trimming the curved composite structural element.23. The method of claim 1, further comprising the step of transferringthe resulting layup comprising the splice onto a curved, concavemanufacturing tool, the curved, concave manufacturing tool having ashape conforming to an external surface of the resulting layup.
 24. Themethod of claim 11, wherein each strip is ⅛ inch wide.
 25. The method ofclaim 12, wherein each strip is between 0.12 inch and 0.25 inch widewhen flattened.